ASTM D3240-22a

• Abstract:

  SIGNIFICANCE AND USE; 5.1 Undissolved (free) water in aviation fuel can encourage the growth of microorganisms and subsequent corrosion in the tanks of aircraft and can also lead to icing of filters in the fuel system. Control of free water is exercised in ground fueling equipment by use of filter-coalescers and water separators.; SCOPE; 1.1 This test method covers the measurement of undissolved water in aviation turbine fuels in flowing fuel streams without exposing the fuel sample to the atmosphere or to a sample container. The usual range of test readings covers from 1 ppm to 60 ppm of free water. This test method does not detect water dissolved in the fuel, and thus test results for comparable fuel streams can vary with fuel temperature and the degree of water solubility in the fuel. ; 1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. ; 1.3 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

• Status: Published
• Publication Date: 30-Jun-2022
• ICS: 75.160.20 - Liquid fuels
• Technical Committee: D02 - Petroleum Products, Liquid Fuels, and Lubricants
• Drafting Committee: D02.J0.05 - Fuel Cleanliness

• Refers: ASTM D4175-23a - Standard Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants
• Effective Date: 15-Dec-2023
• Refers: ASTM D4175-23e1 - Standard Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants
• Effective Date: 01-Jul-2023

Overview

ASTM D3240-22a: Standard Test Method for Undissolved Water In Aviation Turbine Fuels establishes procedures to determine the amount of undissolved (free) water in aviation turbine fuels. Accurate detection of free water is critical for aviation safety, as even small amounts of undissolved water can promote microbial growth leading to corrosion, and can cause filter icing within aircraft fuel systems. This method allows for on-site measurement directly from flowing fuel streams, avoiding sample exposure to the atmosphere or containers, which could affect results.

This ASTM standard supports quality control and operational safety throughout the fuel supply chain, assisting organizations in maintaining safe and reliable aviation operations.

Key Topics

• Undissolved (Free) Water Definition
  • Free water refers to water not dissolved in the fuel, distinct from water that is fully mixed at a molecular level.
• Measurement Range
  • The test method quantifies free water within the range of 1 ppm to 60 ppm by volume.
• Test Apparatus
  • Utilizes uranine dye-treated filter pads, which fluoresce under ultraviolet (UV) or LED light when in contact with free water.
  • The fluorescence level is compared to standards using calibrated instruments to determine water content.
• Sampling Methodology
  • Fuel samples are extracted dynamically from the fuel line, ensuring results reflect the in-line condition without atmospheric exposure.
• Importance of Control
  • Strict control of free water content prevents microbial contamination, corrosion, and operational hazards such as filter icing in aircraft.
• Calibration and Precision
  • Requires calibration with known standards for accurate, repeatable results.
  • Repeatability and reproducibility are measured to verify testing consistency.

Applications

• Aviation Fuel Quality Control
  • Widely used by airports, fuel suppliers, and maintenance crews for regular monitoring of turbine fuels, ensuring compliance with industry safety standards.
• Fuel System Maintenance
  • Essential in routine and pre-flight fuel checks to prevent water-induced failures or efficiency loss in aircraft engines.
• Operational Safety and Compliance
  • Supports compliance with regulatory requirements concerning aviation fuel cleanliness, as mandated by agencies such as the U.S. Department of Defense.
• Ground Fueling Operations
  • Integral part of ground equipment management, including filter-coalescers and water separators, by confirming their effectiveness at removing water.

Related Standards

• ASTM D4175 - Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants, provides key definitions referenced in ASTM D3240.
• ISO Fuel Quality Standards - International standards regulating jet fuel quality may reference or complement methodologies found in ASTM D3240.
• Industry Best Practices for Aviation Fuel Systems - Guides and technical recommendations for safe fuel handling and storage frequently cite ASTM D3240 as a method for water detection.

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Keywords: undissolved water, free water, aviation turbine fuel, ASTM D3240, fuel contamination, filter icing, aviation fuel testing, fuel safety, uranine dye, fluorescence, fuel system maintenance, quality control.

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D3240 − 22a
Standard Test Method for
Undissolved Water In Aviation Turbine Fuels
This standard is issued under the fixed designation D3240; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope* 3.2.2 FreeWaterIndependentofPadReader(FWIPR),n—a
calculated result which provides free water independent of test
1.1 Thistestmethodcoversthemeasurementofundissolved
pad reader used for measurement. FWIPR equations were
water in aviation turbine fuels in flowing fuel streams without
developed from the 2011 ILS data.
exposing the fuel sample to the atmosphere or to a sample
container. The usual range of test readings covers from 1 ppm
4. Summary of Test Method
to 60 ppm of free water.This test method does not detect water
4.1 Ameasured sample of fuel is passed through as uranine
dissolved in the fuel, and thus test results for comparable fuel
dye-treated filter pad. Undissolved (free) water in the fuel will
streams can vary with fuel temperature and the degree of water
react with the uranine dye. When the pad is subsequently
solubility in the fuel.
illuminated by ultraviolet (UV) light, the dye previously
1.2 This standard does not purport to address all of the
contacted by free water will fluoresce a bright yellow with the
safety concerns, if any, associated with its use. It is the
brightness increasing for increasing amounts of free water in
responsibility of the user of this standard to establish appro-
the fuel. The light-illuminated pad is compared to a known
priate safety, health, and environmental practices and deter-
standardusingaphotocellcomparator,andthefreewaterinthe
mine the applicability of regulatory limitations prior to use.
fuel sample is read out in parts per million by volume. By
1.3 This international standard was developed in accor-
varying the fuel sample size, the range of the test method can
dance with internationally recognized principles on standard-
be increased.
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
5. Significance and Use
mendations issued by the World Trade Organization Technical
5.1 Undissolved (free) water in aviation fuel can encourage
Barriers to Trade (TBT) Committee.
the growth of microorganisms and subsequent corrosion in the
tanks of aircraft and can also lead to icing of filters in the fuel
2. Referenced Documents
system. Control of free water is exercised in ground fueling
2.1 ASTM Standards:
equipment by use of filter-coalescers and water separators.
D4175 Terminology Relating to Petroleum Products, Liquid
Fuels, and Lubricants
6. Apparatus
4,5,6,7
6.1 Test Pad Rater (UV Source Device)—A device for
3. Terminology
comparingthefluorescenceofthetestpadtoaknownstandard,
3.1 Definitions:
while both are illuminated by the same source of UV light,
3.1.1 For definitions of terms used in this test method, refer
shall be used. The amount of UV light striking the standard
to Terminology D4175.
shall be modulated until the total fluorescence of the test pad
3.2 Definitions of Terms Specific to This Standard:
3.2.1 free water, n—water not dissolved in the fuel.
Supporting data have been filed at ASTM International Headquarters and may
beobtainedbyrequestingResearchReportRR:D02-1804.ContactASTMCustomer
This test method is under the jurisdiction of ASTM Committee D02 on Service at [e-mail].
Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of The Aqua-Glo Series II instrument manufactured by Gammon Technical
Subcommittee D02.J0.05 on Fuel Cleanliness. Products, Inc., P.O. Box 400, Manasquan, NJ 08736-0400 was used in the original
Current edition approved July 1, 2022. Published September 2022. Originally precision test program (RR:D02-1195). The unit is currently available in a Series V
approved in 1973. Last previous edition approved in 2022 as D3240 – 22. DOI: configuration, which is changed only in the power supply. All water content
10.1520/D3240-22A. measuring components remain of the same configuration as the Series II instrument.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or Manufacturers who wish to offer similar products are referred to Committee D02
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Equipment Replacement Guidelines.
Standards volume information, refer to the standard’s Document Summary page on The sole source of supply of the apparatus known to the committee at this time
the ASTM website. is Gammon Technical Products Inc., P.O. Box 400, Manasquan, NJ 08736-0400.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D3240 − 22a
and the standard are equal; this shall be determined using a 6.8 Calibrating Standard (UV Source Device)—Field cali-
photocell bridge circuit null indicator. The light modulating bration of the instrument should be performed using a calibrat-
device for controlling the UV light striking the standard shall ing standard of known values.
provide a direct reading in parts per million by volume of free
6.9 Calibrating Standard (LED Source Device)—Factory
water.
calibration of the device shall be performed as prescribed in
7,8
6.2 Test Pad Rater (LED Source Device)—A device for Section 9.
rating the fluorescence of the test pad directly by illumination
6.10 Field Verification (LED Source Device)—If the opera-
by a narrow band light source provided by colored LED’s. The
tion of the instrument needs to be verified, an unused pad may
total fluorescence of the test pad is measured directly using a
be inserted for reading; the value shall be less than 0.5 ppm.A
photo sensitive transistor. The intensity of the fluorescence
reference target, available from the manufacturer, when in-
measurement is converted by the device and shall provide a
serted into the device shall read within the limits printed on the
direct reading in parts per million by volume of free water.
rear of the reference target.
6.3 Test Pads—Absorbent filter disks of 25 mm diameter
7. Sampling
shall be coated on one side with uranine (sodium fluorescein)
dye at a concentration of 0.23 mg to 0.29 mg per 25 mm pad.
7.1 The following procedure is applicable for dynamic line
5,9
The test pads shall be individually packaged in hermetically
samples only; that is, taking the fuel sample directly from the
sealed envelopes or other suitable containers. Fresh, unused
test system and through the test pad without exposing the
test pads shall have an orange color over the dyed surface.Any
sample to the atmosphere or to a sample container. The use of
discoloration, unevenness in dye content, or faded (to a yellow
sample containers such as bottles or cans for the temporary
color) appearance shall be cause for rejection.
storage of the sample will result in large errors and is not
5,10
recommended.
6.4 Test Pad Holder and Sampling Line—A test pad
holder and sampling line shall be used to draw the fuel sample
NOTE 1—The amount of free water in a sample is very sensitive to the
through the test pad at a rate of 600 mL⁄min to 800 mL⁄min.
temperature of the sample.The use of sample containers such as bottles or
cans can result in large errors due to changes in sample temperature,
Means shall be provided to flush the test pad sampling line and
adsorption of water on container walls, etc.
holder immediately prior to use. The test pad holder shall
include an orifice of 1 mm (0.040 in.) diameter upstream of the 7.2 Attach the test pad holder assembly to the sampling port
pad to disperse water droplets in the fuel. on the system.
6.5 Tweezers—Suitable clean, dry tweezers shall be used at 7.3 Flush the test pad holder assembly immediately prior to
all times when handling the test pad. sampling, displacing the sampling line with at least two
volumes of test fuel.
6.6 Blotting Paper—Clean, dry, absorbent paper towels,
blotters, etc., shall be provided for blotting the test pad prior to 7.4 Remove the sampling assembly, open the pad holder,
rating to remove excess fuel. The blotter paper shall neither and insert the new test pad using tweezers making sure that the
impart color or stain nor leave any residue on the test pads.
treated side of the test pad is facing upstream. Installation of a
three-way valve immediately upstream of the test pad holder
6.7 Sampling Valve Connection, designed to meet the fol-
will permit flushing with the test pad in place.
lowing requirements: (1) It shall be mounted in the sampling
point and must incorporate a self-sealing quick action coupling
NOTE 2—Do not remove the test pad from the hermetically sealed
package until ready for use. Do not allow any discrete water droplets to
designed to mate with a suitable connection leading to the
come into contact with the pad (from rain, sneezing, coughing, etc.).
selector valve of the sampling assembly. (2) It must be
Exposure of the test pad to the atmosphere, especially on humid days, will
completely resistant to fuel and be leak proof up to the
also ruin the pad in a matter of minutes.
maximum working pressures to be encountered. (3) It must
7.5 Pass 500 mL of fuel through the pad, accurately mea-
have a minimum of internal recesses which could cause the
suring the test sample quantity. Normal sample volume is
holdup of contaminant. (4) It must be provided with a dust cap.
500 mLoftestfuel,butifthereadingisoffscale(onhighside),
sample volumes down to 100 mL in volume may be used. In
The Digital Aqua-Glo (trademarked) instrument is manufactured by Gammon
the latter case, a small graduated cylinder should be used to
Technical Products, Inc., P.O. Box 400, Manasquan, NJ 08736-0400.At instrument
measure the sample volume.
start-up, the display of software version 5.0 indicates that the electronic settings of
the prototype units utilized in the 2011 ILS are in use. Because the electronic
7.6 Measure and record the temperature of the sample.
settings were not optizimed at the time of the 2011 ILS, these units are only
permitted to display calculated FWIPR results. Gammon Technical Products is
8. Calibration (UV Source Devices)
working toward ASTM approval of Digital Aqua-Glo instruments with optimized
electronic settings.
5,11
8.1 Aqua-Glo—The calibrating standard corresponding
If you are aware of alternative suppliers, please provide this information to
to a given undissolved water content is placed in the test pad
ASTM International Headquarters. Your comments will receive careful consider-
ation at a meeting of the responsible technical committee, which you may attend.
window. Turn on the lamp and press the photocell comparator
The sole source of supply of the LED Source Device JF-WA1 instrument
button. Zero the photocell comparator by adjusting the light
known to the committee at this time is manufactured by D-2 Incorporated, 19
CommerceParkRoad,Pocasset,MA02559.Thisinstrumentwasusedinaprecision
test program; reference Research Report RR:D02-1712.
9 11
Aqua-Glo test pads were used in the Precision Test Program. Replacement calibrating standards, but only if the fluorescing standard for the
A test pad holder was used in the Preci
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D3240 − 22 D3240 − 22a
Standard Test Method for
Undissolved Water In Aviation Turbine Fuels
This standard is issued under the fixed designation D3240; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope*
1.1 This test method covers the measurement of undissolved water in aviation turbine fuels in flowing fuel streams without
exposing the fuel sample to the atmosphere or to a sample container. The usual range of test readings covers from 1 ppm to 60 ppm
of free water. This test method does not detect water dissolved in the fuel, and thus test results for comparable fuel streams can
vary with fuel temperature and the degree of water solubility in the fuel.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.3 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D4175 Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants
3. Terminology
3.1 Definitions:
3.1.1 For definitions of terms used in this test method, refer to Terminology D4175.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 free water, n—water not dissolved in the fuel.
3.2.2 Free Water Independent of Pad Reader (FWIPR), n—a calculated result which provides free water independent of test pad
reader used for measurement. FWIPR equations were developed from the 2011 ILS data.
This test method is under the jurisdiction of ASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcommittee
D02.J0.05 on Fuel Cleanliness.
Current edition approved April 1, 2022July 1, 2022. Published May 2022September 2022. Originally approved in 1973. Last previous edition approved in 20152022 as
D3240 – 15.D3240 – 22. DOI: 10.1520/D3240-22.10.1520/D3240-22A.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Supporting data have been filed at ASTM International Headquarters and may be obtained by requesting Research Report RR:D02-1804. Contact ASTM Customer
Service at [e-mail].
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D3240 − 22a
4. Summary of Test Method
4.1 A measured sample of fuel is passed through as uranine dye-treated filter pad. Undissolved (free) water in the fuel will react
with the uranine dye. When the pad is subsequently illuminated by ultraviolet (UV) light, the dye previously contacted by free
water will fluoresce a bright yellow with the brightness increasing for increasing amounts of free water in the fuel. The
light-illuminated pad is compared to a known standard using a photocell comparator, and the free water in the fuel sample is read
out in parts per million by volume. By varying the fuel sample size, the range of the test method can be increased.
5. Significance and Use
5.1 Undissolved (free) water in aviation fuel can encourage the growth of microorganisms and subsequent corrosion in the tanks
of aircraft and can also lead to icing of filters in the fuel system. Control of free water is exercised in ground fueling equipment
by use of filter-coalescers and water separators.
6. Apparatus
4,5,6,7
6.1 Test Pad Rater (UV Source Device)—A device for comparing the fluorescence of the test pad to a known standard, while
both are illuminated by the same source of UV light, shall be used. The amount of UV light striking the standard shall be modulated
until the total fluorescence of the test pad and the standard are equal; this shall be determined using a photocell bridge circuit null
indicator. The light modulating device for controlling the UV light striking the standard shall provide a direct reading in parts per
million by volume of free water.
7,8
6.2 Test Pad Rater (LED Source Device)—A device for rating the fluorescence of the test pad directly by illumination by a
narrow band light source provided by colored LED’s. The total fluorescence of the test pad is measured directly using a photo
sensitive transistor. The intensity of the fluorescence measurement is converted by the device and shall provide a direct reading
in parts per million by volume of free water.
6.3 Test Pads—Absorbent filter disks of 25 mm diameter shall be coated on one side with uranine (sodium fluorescein) dye at a
5,9
concentration of 0.23 mg to 0.29 mg per 25 mm pad. The test pads shall be individually packaged in hermetically sealed
envelopes or other suitable containers. Fresh, unused test pads shall have an orange color over the dyed surface. Any discoloration,
unevenness in dye content, or faded (to a yellow color) appearance shall be cause for rejection.
5,10
6.4 Test Pad Holder and Sampling Line—A test pad holder and sampling line shall be used to draw the fuel sample through
the test pad at a rate of 600 mL ⁄min to 800 mL ⁄min. Means shall be provided to flush the test pad sampling line and holder
immediately prior to use. The test pad holder shall include an orifice of 1 mm (0.040 in.) diameter upstream of the pad to disperse
water droplets in the fuel.
6.5 Tweezers—Suitable clean, dry tweezers shall be used at all times when handling the test pad.
6.6 Blotting Paper—Clean, dry, absorbent paper towels, blotters, etc., shall be provided for blotting the test pad prior to rating to
remove excess fuel. The blotter paper shall neither impart color or stain nor leave any residue on the test pads.
6.7 Sampling Valve Connection, designed to meet the following requirements: (1) It shall be mounted in the sampling point and
The Aqua-Glo Series II instrument manufactured by Gammon Technical Products, Inc., P.O. Box 400, Manasquan, NJ 08736-0400 was used in the original precision
test program (RR:D02-1195). The unit is currently available in a Series V configuration, which is changed only in the power supply. All water content measuring components
remain of the same configuration as the Series II instrument. Manufacturers who wish to offer similar products are referred to Committee D02 Equipment Replacement
Guidelines.
The sole source of supply of the apparatus known to the committee at this time is Gammon Technical Products Inc., P.O. Box 400, Manasquan, NJ 08736-0400.
The Digital Aqua-Glo (trademarked) instrument is manufactured by Gammon Technical Products, Inc., P.O. Box 400, Manasquan, NJ 08736-0400. At instrument start-up,
the display of software version 5.0 indicates that the electronic settings of the prototype units utilized in the 2011 ILS are in use. Because the electronic settings were not
optizimed at the time of the 2011 ILS, these units are only permitted to display calculated FWIPR results. Gammon Technical Products is working toward ASTM approval
of Digital Aqua-Glo instruments with optimized electronic settings.
If you are aware of alternative suppliers, please provide this information to ASTM International Headquarters. Your comments will receive careful consideration at a
meeting of the responsible technical committee, which you may attend.
The sole source of supply of the LED Source Device JF-WA1 instrument known to the committee at this time is manufactured by D-2 Incorporated, 19 Commerce Park
Road, Pocasset, MA 02559. This instrument was used in a precision test program; reference Research Report RR:D02-1712.
Aqua-Glo test pads were used in the Precision Test Program.
A test pad holder was used in the Precision Test Program.
D3240 − 22a
must incorporate a self-sealing quick action coupling designed to mate with a suitable connection leading to the selector valve of
the sampling assembly. (2) It must be completely resistant to fuel and be leak proof up to the maximum working pressures to be
encountered. (3) It must have a minimum of internal recesses which could cause the holdup of contaminant. (4) It must be provided
with a dust cap.
6.8 Calibrating Standard (UV Source Device)—Field calibration of the instrument should be performed using a calibrating
standard of known values.
6.9 Calibrating Standard (LED Source Device)—Factory calibration of the device shall be performed as prescribed in Section 89.
6.10 Field Verification (LED Source Device)—If the operation of the instrument needs to be verified, an unused pad may be
inserted for reading; the value shall be less than 0.5 ppm. A reference target, available from the manufacturer, when inserted into
the device shall read within the limits printed on the rear of the reference target.
7. Sampling
7.1 The following procedure is applicable for dynamic line samples only; that is, taking the fuel sample directly from the test
system and through the test pad without exposing the sample to the atmosphere or to a sample container. The use of sample
containers such as bottles or cans for the temporary storage of the sample will result in large errors and is not recommended.
NOTE 1—The amount of free water in a sample is very sensitive to the temperature of the sample. The use of sample containers such as bottles or cans
can result in large errors due to changes in sample temperature, adsorption of water on container walls, etc.
7.2 Attach the test pad holder assembly to the sampling port on the system.
7.3 Flush the test pad holder assembly immediately prior to sampling, displacing the sampling line with at least two volumes of
test fuel.
7.4 Remove the sampling assembly, open the pad holder, and insert the new test pad using tweezers making sure that the treated
side of the test pad is facing upstream. Installation of a three-way valve immediately upstream of the test pad holder will permit
flushing with the test pad in place.
NOTE 2—Do not remove the test pad from the hermetically sealed package until ready for use. Do not allow any discrete water droplets to come into
contact with the pad (from rain, sneezing, coughing, etc.). Exposure of the test pad to the atmosphere, especially on humid days, will also ruin the pad
in a matter of minutes.
7.5 Pass 500 mL of fuel through the pad, accurately measuring the test sample quantity. Normal sample volume is 500 mL of test
fuel, but if the reading is off scale (on high side), sample volumes down to 100 mL in volume may be used. In the latter case, a
small graduated cylinder should be used to measure the sample volume.
7.6 Measure and record the temperature of the sample.
8. Calibration (UV Source Devices)
5,11
8.1 Aqua-Glo—The calibrating standard corresponding to a given undissolved water content is placed in the test pad window.
Turn on the lamp and press the photocell comparator button. Zero the photocell comparator by adjusting the light m
...